This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2001-071102, filed Mar. 13, 2001, the entire contents of which are incorporated herein by reference.
1. Field of the Invention
This invention relates to a method of and apparatus for measuring the thickness of a film formed on multilayer wiring or the like of a semiconductor wafer and a method of and apparatus for measuring a step height formed in the film. This invention further relates to a program for causing a computer to make such measurements.
2. Description of the Related Art
It has been common practice to measure the thickness of a film formed on multilayer wiring or a step in the film after calibrating the spectral characteristic of the hardware of the optical system, with an Si wafer as a reference. This method, however, has the following problems: it requires a very long time to do calculations because there are many parameters; and high-accuracy measurements cannot be made because there are many uncertain factors, including scattered light developed at the edge of the wiring, the shape of the wiring, and density.
For this reason, there has been a need to realize a film thickness measuring and a step height measuring method and a film thickness measuring apparatus which shorten the time required for calculations by decreasing the number of parameters necessary to measure the film thickness and step height and which make high-accuracy measurements by eliminating such uncertain factors as scattered light developing at the edge of the wiring, the shape of the wiring, and density.
According to a first aspect of the present invention, there is provided a film thickness measuring method comprising: projecting white light onto a wafer with a film to be measured and sensing a first reflected light intensity from the wafer for each wavelength; determining a value of the sensed first reflected light intensity for each wavelength in a form of a first light intensity profile with wavelength as an abscissa axis (x axis) and light intensity as an ordinate axis (y axis); projecting the white light onto a reference sample which has the same structure as that of an underlying layer below a film to be measured of the wafer and sensing a second reflected light intensity from the reference sample for each wavelength; determining a value of the second reflected light intensity for each wavelength in a form of a second light intensity profile with wavelength as the abscissa axis and light intensity as the ordinate axis; calculating a normalized light intensity profile by dividing the first light intensity profile by the second light intensity profile; and calculating the film thickness of the film to be measured from the normalized light intensity profile.
According to a second aspect of the present invention, there is provided a step height measuring method comprising: projecting white light onto a wafer with a film to be measured whose surface is uneven and sensing a first reflected light intensity from the wafer for each wavelength; determining a value of the sensed first reflected light intensity for each wavelength in a form of a first light intensity profile with wavelength as an abscissa axis and light intensity as an ordinate axis; projecting the white light onto a reference sample which has the same structure as that of an underlying layer below a film to be measured of the wafer and sensing a second reflected light intensity from the reference sample for each wavelength; determining a value of the second reflected light intensity for each wavelength in a form of a second light intensity profile with wavelength as the abscissa axis and light intensity as the ordinate axis; calculating a normalized light intensity profile by dividing the first light intensity profile by the second light intensity profile; and calculating a step height in the film to be measured from the normalized light intensity profile.
According to a third aspect of the present invention, there is provided a semiconductor device manufacturing method comprising: forming a film to be measured on a wafer; projecting white light onto the wafer with the film to be measured and sensing a first reflected light intensity from the wafer for each wavelength; determining a value of the sensed first reflected light intensity for each wavelength in a form of a first light intensity profile with wavelength as an abscissa axis and light intensity as an ordinate axis; projecting the white light onto a reference sample which has the same structure as that of an underlying layer below a film to be measured of the wafer and sensing a second reflected light intensity from the reference sample for each wavelength; determining a value of the second reflected light intensity for each wavelength in a form of a second light intensity profile with wavelength as the abscissa axis and light intensity as the ordinate axis; calculating a normalized light intensity profile by dividing the first light intensity profile by the second light intensity profile; calculating the film thickness of the film to be measured from the normalized light intensity profile; and, if the film thickness of the film to be measured meets a process specification, proceeding to the next process, whereas if the film thickness does not meet the process specification, reexamining a condition for manufacturing the film to be measured.
According to a fourth aspect of the present invention, there is provided a film thickness measuring apparatus comprising: a lighting optical system which causes a convergent lens to converge and project white light from a white light source onto a wafer with a film to be measured; a sensor which senses a reflected light intensity from the wafer obtained as a result of the projection of the white light, for each wavelength via a spectroscope; and a computer which calculates a film thickness of the film to be measured, from the sensed reflected light intensity, wherein the computer determines and records the value of the reflected light intensity for each wavelength in a form of a first light intensity profile with wavelength as an abscissa axis and light intensity as an ordinate axis, uses the lighting optical system and the sensor to calculate and record in a form of a second light intensity profile the reflected light intensity from a reference sample which has the same structure as that of an underlying layer below the film to be measured, calculates a normalized light intensity profile by dividing the first light intensity profile by the second light intensity profile, and calculates a film thickness of the film to be measured from the normalized light intensity profile.
According to a fifth aspect of the present invention, there is provided a computer program recorded on a computer-readable medium, configured to measure a film thickness of a film to be measured on a wafer, the computer program comprising: projecting white light onto a wafer with a film to be measured and sensing a first reflected light intensity from the wafer for each wavelength; determining a value of the sensed first reflected light intensity for each wavelength in a form of a first light intensity profile with wavelength as an abscissa axis and light intensity as an ordinate axis; projecting the white light onto a reference sample which has the same structure as that of the underlying layer below the film to be measured of the wafer and sensing a second reflected light intensity from the reference sample for each wavelength; determining a value of the second reflected light intensity for each wavelength in a form of a second light intensity profile with wavelength as the abscissa axis and light intensity as the ordinate axis; calculating a normalized light intensity profile by dividing the first light intensity profile by the second light intensity profile; and calculating a film thickness of the film to be measured from the normalized light intensity profile.